Variable valve timing systems for overhead camshaft engines are known in the art. Such systems include a target wheel to indicate the rotational position of the camshaft, and a phaser assembly to alter the rotational position of the camshaft relative to the crankshaft. In order to function properly, the target wheel should rotate in exact synchronization with the camshaft. Current sensor systems use a target wheel mounted on the front or rear end of the camshaft causing an increase in the effective length of the camshaft, and requiring an increase in the overall length of the head. Since the camshaft phaser is normally mounted on the end of the camshaft and the outer periphery of many phaser housings do not rotate, mounting the target wheel on the phaser housing is not suitable. Some engine designs use a rotating PCV valve that is mounted on the end of the camshaft, precluding the use of the camshaft end for the target wheel. Alternatively, the target wheel may be attached to the timing gears. However, a target wheel that is attached to the timing gears often does not give accurate readings of the position of the camshaft because of the play in the timing gear mechanism.
The rotational position of the target wheel has to be read by a sensor. When the target wheel is mounted on the end of the camshaft, a hole has to be made in the head of the engine, and the sensor is mounted in the hole. Each hole has to be drilled and tapped for reception of the sensor, and sealed after the sensor is mounted therein. For an I-configuration engine with dual overhead cams, two mounting holes are required; for a V-configuration engine, four mounting holes are required.